.box1{
    /* width: 300px; */
    height: 200px;
    display: flex;
}
.box1 ._left {
    height: 100%;
    width: 30px;
    background: green;
}
.box1 ._right {
    height: 100%;
    /* width: 80%; */
    background: blue;
    display: flex;
    flex: 2;
}
.box1 ._3 {
    height: 100%;
    width: 30px;
    background: green;
}